Describing the distribution patterns of organisms and factors that control them is central to the study of ecology and historically has been the focus of many limnological studies. An entire field, conservation biology, is now dedicated to the science of conserving organisms. We are living in a time of unprecedented rates of human-caused extinction, particularly in freshwater habitats. Efforts to understand, manage, or conserve species require knowledge of distribution of organisms in their habitats, how they evolved, and how they maintain populations. In addition to causing many species to go extinct and threatening many more, people are introducing exotic species into habitats at very high rates. Species introductions can lead to direct negative effects on humans and often harm the ecosystems that exotic species invade. In this chapter, we discuss measures of diversity and how and why diversity varies among and within habitats, and we describe some particularly spectacular cases of high diversity. We also discuss extinctions caused by humans and some of the associated consequences, as well as consequences of invasive species.
Freshwater Ecology, Third Edition, Aquatic Ecology, 2020, Pages 295-333,